Effects of diabetes-induced hyperglycemia on epigenetic modifications and DNA packaging and methylation during spermatogenesis; A narrative review

Document Type : Review Article

Authors

1 Department of Surgery, Division of Urology, Human Reproduction Section, São Paulo Federal University, São Paulo, Brazil

2 Department of Anatomy and UMIB - Unit for Multidisciplinary Research in Biomedicine, ICBAS - School of Medicine and Biomedical Sciences, University of Porto, Porto, Portugal

Abstract

The impact of diabetes on various organs failure including testis has been highlighted during the last decades. If on one hand diabetes-induced hyperglycemia has a key role in induced damages; on the other hand, glucose deprivation plays a key role in inducing male infertility. Indeed, glucose metabolism during spermatogenesis has been highlighted due to post-meiotic germ cells drastic dependence on glucose-derived metabolites, especially lactate. In fact, hyperglycemia-induced spermatogenesis arrest has been demonstrated in various studies. Moreover, various sperm maturation processes related to sperm function such as motility are directly depending on glucose metabolism in Sertoli cells. It has been demonstrated that diabetes-induced hyperglycemia adversely impacts sperm morphology, motility and DNA integrity, leading to infertility. However, fertility quality is another important factor to be considered. Diabetes-induced hyperglycemia is not only impacting sperm functions, but also affecting sperm epigenome.  DNA packing process and epigenetics modifications occur during spermatogenesis process, determining next generation genetic quality transmitted through sperm. Critical damages may occur due to under- or downregulation of key proteins during spermatogenesis. Consequently, unpacked DNA is more exposed to oxidative stress, leading to intensive DNA damages. Moreover, epigenetic dysregulation occurred during spermatogenesis may impact embryo quality and be transmitted to next generations, increasing offspring genetic issues. Herein we discuss the mechanisms by which diabetes-induced hyperglycemia can affect epigenetic modifications and DNA packaging and methylation during spermatogenesis thus promoting long-lasting effects to the next generation. 

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Main Subjects


1. Zegers-Hochschild F, Adamson GD, de Mouzon J, Ishihara O, Mansour R, Nygren K, et al. International Committee for Monitoring Assisted Reproductive Technology (ICMART) and the World Health Organization (WHO) revised glossary of ART terminology, 2009. Fertil Steril 2009; 92:1520-1524.
2. Minas A, Costa LVS, Miyazaki MA, Antoniassi MP. Insight toward inflammasome complex contribution to male infertility. Am J Reprod Immunol 2023; 90:e13734.
3. Alves MG, Martins AD, Cavaco JE, Socorro S, Oliveira PF. Diabetes, insulin-mediated glucose metabolism and Sertoli/blood-testis barrier function. Tissue Barriers 2013; 1:e23992.
4. Saeedi P, Petersohn I, Salpea P, Malanda B, Karuranga S, Unwin N, et al. Global and regional diabetes prevalence estimates for 2019 and projections for 2030 and 2045: Results from the International Diabetes Federation Diabetes Atlas, 9th edition. Diabetes Research and Clinical Practice 2019; 157.
5. Pereira SC, Crisóstomo L, Sousa M, Oliveira PF, Alves MG. Metabolic diseases affect male reproduction and induce signatures in gametes that may compromise the offspring health. Environ Epigenet 2020; 6:dvaa019.
6. Coppell KJ, Abel S, Whitehead LC, Tangiora A, Spedding T, Tipene-Leach D. A diagnosis of prediabetes when combined with lifestyle advice and support is considered helpful rather than a negative label by a demographically diverse group: A qualitative study. Prim Care Diabetes 2021.
7. Organization WH. Definition and diagnosis of diabetes mellitus and intermediate hyperglycaemia: report of a WHO/IDF consultation.  2006.
8. Agbaje I, McVicar C, Schock B, McClure N, Atkinson AB, Rogers D, et al. Increased concentrations of the oxidative DNA adduct 7, 8-dihydro-8-oxo-2-deoxyguanosine in the germ-line of men with type 1 diabetes. Reproductive biomedicine online 2008; 16:401-409.
9. Maresch CC, Stute DC, Alves MG, Oliveira PF, de Kretser DM, Linn T. Diabetes-induced hyperglycemia impairs male reproductive function: a systematic review. Human Reproduction Update 2018; 24:86-105.
10. Bhattacharya SM, Ghosh M, Nandi N. Diabetes mellitus and abnormalities in semen analysis. J Obstet Gynaecol Res 2014; 40:167-171.
11. Giugliano F, Maiorino M, Bellastella G, Gicchino M, Giugliano D, Esposito K. Determinants of erectile dysfunction in type 2 diabetes.  Int J Impot Res 2010; 22:204-209.
12. Aeeni M, Razi M, Alizadeh A, Alizadeh A. The molecular mechanism behind insulin protective effects on testicular tissue of hyperglycemic rats. Life Sciences 2021; 277:119394.
13. Khavarimehr M, Nejati V, Razi M, Najafi G. Ameliorative effect of omega-3 on spermatogenesis, testicular anti-oxidant status and preimplantation embryo development in streptozotocin-induced diabetes in rats. International urology and nephrology 2017; 49:1545-1560.
14. Samie A, Sedaghat R, Baluchnejadmojarad T, Roghani M. Hesperetin, a citrus flavonoid, attenuates testicular damage in diabetic rats via inhibition of oxidative stress, inflammation, and apoptosis. Life sciences 2018; 210:132-139.
15. Ding G-L, Liu Y, Liu M-E, Pan J-X, Guo M-X, Sheng J-Z, et al. The effects of diabetes on male fertility and epigenetic regulation during spermatogenesis. Asian J Androl 2015; 17:948.
16. Muratori M, Tamburrino L, Marchiani S, Cambi M, Olivito B, Azzari C, et al. Investigation on the Origin of Sperm DNA Fragmentation: Role of Apoptosis, Immaturity and Oxidative Stress. Mol Med 2015; 21:109-122.
17. Zysk JR, Bushway AA, Whistler RL, Carlton WW. Temporary sterility produced in male mice by 5-thio-D-glucose. J Reprod Fertil 1975; 45:69-72.
18. Alves MG, Rato L, Carvalho RA, Moreira PI, Socorro S, Oliveira PF. Hormonal control of Sertoli cell metabolism regulates spermatogenesis. Cell Mol Life Sci 2013; 70:777-793.
19. La Vignera S, Calogero A, Condorelli R, Lanzafame F, Giammusso B, Vicari E. Andrological characterization of the patient with diabetes mellitus. Minerva endocrinologica 2009; 34:1-9.
20. Sjöberg L, Pitkäniemi J, Haapala L, Kaaja R, Tuomilehto J. Fertility in people with childhood-onset type 1 diabetes. Diabetologia 2013; 56:78-81.
21. Wiebe JC, Santana A, Medina-Rodríguez N, Hernández M, Nóvoa J, Mauricio D, et al. Fertility is reduced in women and in men with type 1 diabetes: results from the Type 1 Diabetes Genetics Consortium (T1DGC). Diabetologia 2014; 57:2501-2504.
22. Kam J, Tsang VH, Chalasani V. Retrograde Ejaculation: A Rare Presenting Symptom of Type 1 Diabetes Mellitus. Urol Case Rep 2017; 10:9-10.
23. Niven MJ, Hitman GA, Badenoch DF. A study of spermatozoal motility in type 1 diabetes mellitus. Diabet Med 1995; 12:921-924.
24. Paasch U, Heidenreich F, Pursche T, Kuhlisch E, Kettner K, Grunewald S, et al. Identification of increased amounts of eppin protein complex components in sperm cells of diabetic and obese individuals by difference gel electrophoresis. Mol Cell Proteomics 2011; 10:M110.007187.
25. Baccetti B, La Marca A, Piomboni P, Capitani S, Bruni E, Petraglia F, et al. Insulin-dependent diabetes in men is associated with hypothalamo-pituitary derangement and with impairment in semen quality. Hum Reprod 2002; 17:2673-2677.
26. Maric C, Forsblom C, Thorn L, Wadén J, Groop PH. Association between testosterone, estradiol and sex hormone binding globulin levels in men with type 1 diabetes with nephropathy. Steroids 2010; 75:772-778.
27. Crisóstomo L, Rato L, Jarak I, Silva BM, Raposo JF, Batterham RL, et al. A switch from high-fat to normal diet does not restore sperm quality but prevents metabolic syndrome. Reproduction 2019; 158:377-387.
28. Crisóstomo L, Videira RA, Jarak I, Starčević K, Mašek T, Rato L, et al. Diet during early life defines testicular lipid content and sperm quality in adulthood. Am J Physiol Endocrinol Metab 2020; 319:E1061-e1073.
29. Crisóstomo L, Jarak I, Rato LP, Raposo JF, Batterham RL, Oliveira PF, et al. Inheritable testicular metabolic memory of high-fat diet causes transgenerational sperm defects in mice. Sci Rep 2021; 11:9444.
30. Crisóstomo L, Oliveira PF, Alves MG. Sperm, metabolic memory and echoes from Lamarck. Eur J Clin Invest 2021; 51:e13492.
31. Alves MG, Martins AD, Rato L, Moreira PI, Socorro S, Oliveira PF. Molecular mechanisms beyond glucose transport in diabetes-related male infertility. Biochim Biophys Acta 2013; 1832:626-635.
32. Bajpai M, Gupta G, Setty BS. Changes in carbohydrate metabolism of testicular germ cells during meiosis in the rat. Eur J Endocrinol 1998; 138:322-327.
33. Boussouar F, Benahmed M. Lactate and energy metabolism in male germ cells. Trends Endocrinol Metab 2004; 15:345-350.
34. Jutte NH, Grootegoed JA, Rommerts FF, van der Molen HJ. Exogenous lactate is essential for metabolic activities in isolated rat spermatocytes and spermatids. J Reprod Fertil 1981; 62:399-405.
35. Erkkilä K, Aito H, Aalto K, Pentikäinen V, Dunkel L. Lactate inhibits germ cell apoptosis in the human testis. Mol Hum Reprod 2002; 8:109-117.
36. Courtens JL, Plöen L. Improvement of spermatogenesis in adult cryptorchid rat testis by intratesticular infusion of lactate. Biol Reprod 1999; 61:154-161.
37. Schrade A, Kyrönlahti A, Akinrinade O, Pihlajoki M, Fischer S, Rodriguez VM, et al. GATA4 Regulates Blood-Testis Barrier Function and Lactate Metabolism in Mouse Sertoli Cells. Endocrinology 2016; 157:2416-2431.
38. Verma R, Haldar C. Photoperiodic modulation of thyroid hormone receptor (TR-α), deiodinase-2 (Dio-2) and glucose transporters (GLUT 1 and GLUT 4) expression in testis of adult golden hamster, Mesocricetus auratus. J Photochem Photobiol B 2016; 165:351-358.
39. Rato L, Alves MG, Duarte AI, Santos MS, Moreira PI, Cavaco JE, et al. Testosterone deficiency induced by progressive stages of diabetes mellitus impairs glucose metabolism and favors glycogenesis in mature rat Sertoli cells. Int J Biochem Cell Biol 2015; 66:1-10.
40. Pitetti JL, Calvel P, Zimmermann C, Conne B, Papaioannou MD, Aubry F, et al. An essential role for insulin and IGF1 receptors in regulating sertoli cell proliferation, testis size, and FSH action in mice. Mol Endocrinol 2013; 27:814-827.
41. Griffeth RJ, Bianda V, Nef S. The emerging role of insulin-like growth factors in testis development and function. Basic Clin Androl 2014; 24:12.
42. Soudmand P, Tofighi A, Tolouei Azar J, Razi M, Ghaderi Pakdel F. Different continuous exercise training intensities induced effect on sertoli-germ cells metabolic interaction; implication on GLUT-1, GLUT-3 and MCT-4 transporting proteins expression level. Gene 2021; 783:145553.
43. Mateus I, Feijó M, Espínola LM, Vaz CV, Correia S, Socorro S. Glucose and glutamine handling in the Sertoli cells of transgenic rats overexpressing regucalcin: plasticity towards lactate production. Sci Rep 2018; 8:10321.
44. Riera MF, Galardo MN, Pellizzari EH, Meroni SB, Cigorraga SB. Molecular mechanisms involved in Sertoli cell adaptation to glucose deprivation. Am J Physiol Endocrinol Metab 2009; 297:E907-914.
45. Alves MG, Socorro S, Silva J, Barros A, Sousa M, Cavaco JE, et al. In vitro cultured human Sertoli cells secrete high amounts of acetate that is stimulated by 17β-estradiol and suppressed by insulin deprivation. Biochim Biophys Acta 2012; 1823:1389-1394.
46. Hsu S-K, Cheng K-C, Mgbeahuruike MO, Lin Y-H, Wu C-Y, Wang H-MD, et al. New Insight into the Effects of Metformin on Diabetic Retinopathy, Aging and Cancer: Nonapoptotic Cell Death, Immunosuppression, and Effects beyond the AMPK Pathway. Int J Mol Sci 2021; 22:9453.
47. Zhang CS, Jiang B, Li M, Zhu M, Peng Y, Zhang YL, et al. The lysosomal v-ATPase-Ragulator complex is a common activator for AMPK and mTORC1, acting as a switch between catabolism and anabolism. Cell Metab 2014; 20:526-540.
48. Galardo MN, Riera MF, Pellizzari EH, Cigorraga SB, Meroni SB. The AMP-activated protein kinase activator, 5-aminoimidazole-4-carboxamide-1-b-D-ribonucleoside, regulates lactate production in rat Sertoli cells. J Mol Endocrinol 2007; 39:279-288.
49. Tartarin P, Guibert E, Touré A, Ouiste C, Leclerc J, Sanz N, et al. Inactivation of AMPKα1 induces asthenozoospermia and alters spermatozoa morphology. Endocrinology 2012; 153:3468-3481.
50. Hardie DG. AMP-activated/SNF1 protein kinases: conserved guardians of cellular energy. Nat Rev Mol Cell Biol 2007; 8:774-785.
51. Coussens M, Maresh JG, Yanagimachi R, Maeda G, Allsopp R. Sirt1 deficiency attenuates spermatogenesis and germ cell function. PLoS One 2008; 3:e1571.
52. Reznick RM, Shulman GI. The role of AMP-activated protein kinase in mitochondrial biogenesis. J Physiol 2006; 574:33-39.
53. Zhang BB, Zhou G, Li C. AMPK: an emerging drug target for diabetes and the metabolic syndrome. Cell Metab 2009; 9:407-416.
54. Galardo MN, Riera MF, Pellizzari EH, Sobarzo C, Scarcelli R, Denduchis B, et al. Adenosine regulates Sertoli cell function by activating AMPK. Mol Cell Endocrinol 2010; 330:49-58.
55. Azarniad R, Razi M, Hasanzadeh S, Malekinejad H. Experimental diabetes negatively affects the spermatogonial stem cells’ self-renewal by suppressing GDNF network interactions. Andrologia 2020; 52:e13710.
56. Jiang X, Chen J, Zhang C, Zhang Z, Tan Y, Feng W, et al. The protective effect of FGF21 on diabetes-induced male germ cell apoptosis is associated with up-regulated testicular AKT and AMPK/Sirt1/PGC-1α signaling. Endocrinology 2015; 156:1156-1170.
57. Soudamani S, Malini T, Balasubramanian K. Effects of streptozotocin-diabetes and insulin replacement on the epididymis of prepubertal rats: histological and histomorphometric studies. Endocr Res 2005; 31:81-98.
58. Minas A, Talebi H, Taravat Ray M, Yari Eisalou M, Alves MG, Razi M. Insulin treatment to type 1 male diabetic rats protects fertility by avoiding testicular apoptosis and cell cycle arrest. Gene 2021; 799:145847.
59. Scarano WR, Messias AG, Oliva SU, Klinefelter GR, Kempinas WG. Sexual behaviour, sperm quantity and quality after short-term streptozotocin-induced hyperglycaemia in rats. Int J Androl 2006; 29:482-488.
60. Amaral S, Moreno AJ, Santos MS, Seiça R, Ramalho-Santos J. Effects of hyperglycemia on sperm and testicular cells of Goto-Kakizaki and streptozotocin-treated rat models for diabetes. Theriogenology 2006; 66:2056-2067.
61. Hassan AA, Hassouna MM, Taketo T, Gagnon C, Elhilali MM. The effect of diabetes on sexual behavior and reproductive tract function in male rats. J Urol 1993; 149:148-154.
62. Cameron DF, Rountree J, Schultz RE, Repetta D, Murray FT. Sustained hyperglycemia results in testicular dysfunction and reduced fertility potential in BBWOR diabetic rats. Am J Physiol 1990; 259:E881-889.
63. Kim ST, Moley KH. Paternal effect on embryo quality in diabetic mice is related to poor sperm quality and associated with decreased glucose transporter expression. Reproduction 2008; 136:313-322.
64. Tsounapi P, Honda M, Dimitriadis F, Kawamoto B, Hikita K, Muraoka K, et al. Impact of anti-oxidants on seminal vesicles function and fertilizing potential in diabetic rats. Asian J Androl 2017; 19:639-646.
65. Rato L, Alves MG, Dias TR, Cavaco JE, Oliveira PF. Testicular Metabolic Reprogramming in Neonatal Streptozotocin-Induced Type 2 Diabetic Rats Impairs Glycolytic Flux and Promotes Glycogen Synthesis. J Diabetes Res 2015; 2015:973142.
66. Samadian Z, Tofighi A, Razi M, Tolouei Azar J, Ghaderi Pakdel F. Moderate-intensity exercise training ameliorates the diabetes-suppressed spermatogenesis and improves sperm parameters: Insole and simultaneous with insulin. Andrologia 2019; 51:e13457.
67. Palmeira CM, Santos DL, Seiça R, Moreno AJ, Santos MS. Enhanced mitochondrial testicular anti-oxidant capacity in Goto-Kakizaki diabetic rats: role of coenzyme Q. Am J Physiol Cell Physiol 2001; 281:C1023-1028.
68. Yu T, Robotham JL, Yoon Y. Increased production of reactive oxygen species in hyperglycemic conditions requires dynamic change of mitochondrial morphology. Proc Natl Acad Sci U S A 2006; 103:2653-2658.
69. Rato L, Duarte AI, Tomás GD, Santos MS, Moreira PI, Socorro S, et al. Pre-diabetes alters testicular PGC1-α/SIRT3 axis modulating mitochondrial bioenergetics and oxidative stress. Biochim Biophys Acta 2014; 1837:335-344.
70. Koh PO. Streptozotocin-induced diabetes increases apoptosis through JNK phosphorylation and Bax activation in rat testes. J Vet Med Sci 2007; 69:969-971.
71. Koh PO. Streptozotocin-induced diabetes increases the interaction of Bad/Bcl-XL and decreases the binding of pBad/14-3-3 in rat testis. Life Sci 2007; 81:1079-1084.
72. Samadian Z, Azar JT, Moshari S, Razi M, Tofighi A. Moderate-intensity Exercise Training in Sole and Simultaneous Forms with Insulin Ameliorates the Experimental Type 1 Diabetes-induced Intrinsic Apoptosis in Testicular Tissue. Int J Sports Med 2019; 40:909-920.
73. Dias TR, Alves MG, Rato L, Casal S, Silva BM, Oliveira PF. White tea intake prevents prediabetes-induced metabolic dysfunctions in testis and epididymis preserving sperm quality. J Nutr Biochem 2016; 37:83-93.
74. Aitken RJ, Jones KT, Robertson SA. Reactive oxygen species and sperm function--in sickness and in health. J Androl 2012; 33:1096-1106.
75. Roessner C, Paasch U, Kratzsch J, Glander HJ, Grunewald S. Sperm apoptosis signalling in diabetic men. Reprod Biomed Online 2012; 25:292-299.
76. Yigitturk G, Acara AC, Erbas O, Oltulu F, Yavasoglu NUK, Uysal A, et al. The anti-oxidant role of agomelatine and gallic acid on oxidative stress in STZ induced type I diabetic rat testes. Biomed Pharmacother 2017; 87:240-246.
77. Meistrich ML, Hess RA. Assessment of spermatogenesis through staging of seminiferous tubules. Methods Mol Biol 2013; 927:299-307.
78. Nasr Esfahani MH, Tavalaee M. Origin and role of DNA damage in varicocele. Int J Fertil Steril 2012; 6:141-146.
79. Govin J, Caron C, Escoffier E, Ferro M, Kuhn L, Rousseaux S, et al. Post-meiotic shifts in HSPA2/HSP70.2 chaperone activity during mouse spermatogenesis. J Biol Chem 2006; 281:37888-37892.
80. Bukau B, Weissman J, Horwich A. Molecular chaperones and protein quality control. Cell 2006; 125:443-451.
81. Razi M, Tavalaee M, Sarrafzadeh-Rezaei F, Moazamian A, Gharagozloo P, Drevet JR, et al. Varicocoele and oxidative stress: New perspectives from animal and human studies. Andrology 2021; 9:546-558.
82. Khosravanian N, Razi M, Farokhi F, Khosravanian H. Testosterone and vitamin E administration up-regulated varicocele-reduced Hsp70-2 protein expression and ameliorated biochemical alterations. J Assist Reprod Genet 2014; 31:341-354.
83. Rezazadeh-Reyhani Z, Razi M, Malekinejad H, Sadrkhanlou R. Cytotoxic effect of nanosilver particles on testicular tissue: Evidence for biochemical stress and Hsp70-2 protein expression. Environ Toxicol Pharmacol 2015; 40:626-638.
84. Rathke C, Baarends WM, Awe S, Renkawitz-Pohl R. Chromatin dynamics during spermiogenesis. Biochim Biophys Acta 2014; 1839:155-168.
85. Salmani S, Razi M, Sarrafzadeh-Rezaei F, Mahmoudian A. Testosterone amplifies HSP70-2a, HSP90 and PCNA expression in experimental varicocele condition: Implication for DNA fragmentation. Reprod Biol 2020; 20:384-395.
86. Bahmanzadeh M, Goodarzi MT, Rezaei Farimani A, Fathi N, Alizadeh Z. Resveratrol supplementation improves DNA integrity and sperm parameters in streptozotocin-nicotinamide-induced type 2 diabetic rats. Andrologia 2019; 51:e13313.
87. Pavlinkova G, Margaryan H, Zatecka E, Valaskova E, Elzeinova F, Kubatova A, et al. Transgenerational inheritance of susceptibility to diabetes-induced male subfertility. Sci Rep 2017; 7:4940.
88. Blumer CG, Restelli AE, Giudice PT, Soler TB, Fraietta R, Nichi M, et al. Effect of varicocele on sperm function and semen oxidative stress. BJU Int 2012; 109:259-265.
89. Smith R, Kaune H, Parodi D, Madariaga M, Rios R, Morales I, et al. Increased sperm DNA damage in patients with varicocele: relationship with seminal oxidative stress. Hum Reprod 2006; 21:986-993.
90. Kaneda M, Okano M, Hata K, Sado T, Tsujimoto N, Li E, et al. Essential role for de novo DNA methyltransferase Dnmt3a in paternal and maternal imprinting. Nature 2004; 429:900-903.
91. Santi D, De Vincentis S, Magnani E, Spaggiari G. Impairment of sperm DNA methylation in male infertility: a meta‐analytic study. Andrology 2017; 5:695-703.
92. Aoki VW, Emery BR, Carrell DT. Global sperm deoxyribonucleic acid methylation is unaffected in protamine-deficient infertile males. Fertility and sterility 2006; 86:1541-1543.
93. Bahreinian M, Tavalaee M, Abbasi H, Kiani-Esfahani A, Shiravi AH, Nasr-Esfahani MH. DNA hypomethylation predisposes sperm to DNA damage in individuals with varicocele. Syst Biol Reprod Med 2015; 61:179-186.
94. Bose R, Adiga SK, D’Souza F, Salian SR, Uppangala S, Kalthur G, et al. Germ cell abnormalities in streptozotocin induced diabetic mice do not correlate with blood glucose level. J Assist Reprod Genet 2012; 29:1405-1413.
95. El-Behery EI, El-Naseery NI, El-Ghazali HM, Elewa YHA, Mahdy EAA, El-Hady E, et al. The efficacy of chronic zinc oxide nanoparticles using on testicular damage in the streptozotocin-induced diabetic rat model. Acta Histochem 2019; 121:84-93.
96. Santana VP, Miranda-Furtado CL, Pedroso DCC, Eiras MC, Vasconcelos MAC, Ramos ES, et al. The relationship among sperm global DNA methylation, telomere length, and DNA fragmentation in varicocele: a cross-sectional study of 20 cases. Syst Biol Reprod Med 2019; 65:95-104.
97. Moradi-Ozarlou M, Moshari S, Rezaeiagdam H, Nomanzadeh A, Shahmohamadlou S, Razi M. High-fat diet-induced obesity amplifies HSP70-2a and HSP90 expression in testicular tissue; correlation with proliferating cell nuclear antigen (PCNA). Life Sciences 2021; 279.
98. Schermelleh L, Haemmer A, Spada F, Rösing N, Meilinger D, Rothbauer U, et al. Dynamics of Dnmt1 interaction with the replication machinery and its role in postreplicative maintenance of DNA methylation. Nucleic acids research 2007; 35:4301-4312.
99. Spada F, Haemmer A, Kuch D, Rothbauer U, Schermelleh L, Kremmer E, et al. DNMT1 but not its interaction with the replication machinery is required for maintenance of DNA methylation in human cells. J Cell Biol 2007; 176:565-571.
100. Zamudio NM, Chong S, O’Bryan MK. Epigenetic regulation in male germ cells. Reproduction 2008; 136:131-146.